The art of reactor damping of vibratory chattering such as induced by single cutting point boring bars of extensive length is illustrated by applicant's prior application, Ser. No. 379,438, as well as prior U.S. Pat. Nos. 3,207,009; 2,591,115; 3,598,498; and 3,642,378. It is typical of all such prior art to transmit the damping impact in a radial direction transverse to the axis of the boring bar to the surrounding wall of the boring bar either directly or through a viscous fluid occupying the clearance space.